1. Field of the Invention
The present invention relates to a shift lever assembly for application to an electric starter motor for starting an engine.
2. Description of the Related Art
An electric starter motor includes: a starter motor for generating a torque; a planetary reduction assembly for reducing and outputting the torque from the starter motor; an overrunning clutch spline-fitted onto an output shaft of the planetary reduction assembly; a pinion integrated with the overrunning clutch slidably disposed on the output shaft; and an electromagnetic switch for controlling the passage of current to the starter motor and for pushing the pinion together with the overrunning clutch towards a ring gear of an engine by means of a shift lever assembly.
FIG. 12 is an exploded perspective of a conventional shift lever assembly for an electric starter motor, such as that described in Japanese Patent Laid-Open No. 62-28311, for example.
In FIG. 12, the shift lever assembly 50 includes: a lever holder 51 for securing to a front bracket (not shown); a shift lever 53 rotatably supported in the lever holder 51 by means of a pivot pin 52; and a torsion coil spring 54 connected to the shift lever 53 and a hook on a magnetic switch (not shown) so as to be able to impart actuating torque to the shift lever 53, elastically deforming when subjected to a torsional torque above a predetermined value.
The shift lever 53 includes: a first arm 53a for engaging an overrunning clutch (not shown); a forked second arm 53b extending in the opposite direction from the first arm 53a for supporting portions of both ends of the pivot pin 52 in a pair of pin bores 53d on either side; and a bridge portion 53c connecting the forked portions of the second arm 53b in the vicinity of the pin bores 53d.
The torsion coil spring 54 includes: a coil portion 54c inserted with enough play so as not to contact the pivot pin 52; and first and second engaging arms 54a and 54b extending from the coil portion 54c in mutually opposite directions. The first engaging arm 54a engages with the rear surface of the first arm 53a.
The lever holder 51 has a pair of arm portions 51a and 51b for holding the shift lever 53 on either side, pin bores 51c and 51d for supporting both ends of the pivot pin 52 being disposed in the arm portions 51a and 51b. One pin bore 51c is formed with approximately the same diameter as the pivot pin 52, and the other pin bore 51d is formed with a smaller diameter than the pivot pin 52.
To assemble a shift lever assembly 50 constructed in this manner, the torsion coil spring 54 is mounted on the shift lever 53 by first supporting the outer circumference of the coil portion 54c of the torsion coil spring 54 against the front surface of the bridge portion 53c, then engaging the first engaging arm 54a against the rear surface of the first arm 53a while applying a predetermined torsional torque to the coil portion 54c as a set load, and additionally placing the second engaging arm 54b in contact with the rear surfaces of the forked second arm 53b so as to span the two.
Next, the shift lever 53 is inserted between the pair of arms 51a and 51b of the lever holder 51 such that the pin bores 53d and the pin bores 51c and 51d align. Then, the pivot pin 52 is inserted from the pin bore 51c, through the pin bores 53d, and pressed into the pin bore 51d, mounting the shift lever 53 to the lever holder 51 to complete assembly of the shift lever assembly 50.
Then, the shift lever assembly 50 is mounted to the electric starter motor by securing the lever holder 51 to the front bracket.
Because the conventional shift lever assembly for an electric starter motor is constructed in this manner, one problem has been that there are many parts and the shape of the parts is complex, making it difficult to reduce costs.
Because the pivot pin 52 has been prevented from dislodging by pressing the pivot pin 52 into the pin bore 51d, another problem has been that strict precision has been required in the diameter of the pin bore 51d, also making it difficult to reduce costs.
Yet another problem has been difficult assembly because of the need to apply torsional torque to the torsion coil spring 54 while mounting the torsion coil spring on the shift lever 53.